Programing challenge

[Nick Harms]

This is supposed to be a class with a demo. The demo gets the circle radius and sends it to the class to do work and return the circumference, area and diameter.
For some reason when I run the program (I get no errors when compiling) I get o's for my awnsers no matter what radius is used. I think its probably something stupid thing I overlooked, and i need a wiser person than I to help me out!
Much appreciated.

Circle class then demo
Circle Class

   

public class Circle
{
   double radius;
   double PI = 3.14159;
   
   public Circle(double rad)                     
   {

   radius = rad; 

    }


    /**
      The setRadius method gives initial value to the radius from the demo program.
      @param rad The value to store in radius.
   */

   public void setRadius(double rad)
   {
      radius = rad;
   }

   /**
      The getRadius method returns the radius when called.
      @return The value in the radius field.
   */

   public double getRadius()
   {
      return radius;
   }

   /**
      The getWidth method returns a Rectangle
      object's width.
      @return The value in the width field.
   */
   
   public double getArea()
   {
      return PI*radius*radius;
      
   }

   /**
      The getDiameter method returns the diameter of the circle.
      @return The product of radius times 2.
   */

   public double getDiameter()
   {
      return radius * 2;
   }
   
   /**
      The getCircumference method returns the circumference of the circle.
      @return radius times PI times 2.
   */
    
    public double getCircumference()
    {
        return 2 * PI * radius;
    }
}

 

Demo

import java.util.Scanner;

public class CircleDemo
{
   public static void main(String[] args)
   {
      double rad = 0;
      // Create a circle object.
      Circle Circle = new Circle(rad);
      
      // Create a Scanner object for keyboard input.
      Scanner keyboard = new Scanner(System.in);
      
      // Get the radius from user;
      System.out.print("Enter the radius of your circle");
      rad = keyboard.nextDouble();


      // Get data from circle and disply it
      System.out.println("The circle's area is: " + Circle.getArea());
      System.out.println("The circle's diameter is: " + Circle.getDiameter());
      System.out.println("The circle's circumference is: " + Circle.getCircumference()); 
   }
}
   

[Janeice DelVecchio]

What is the demo class supposed to do, in normal person terms, step by step?

Edit: and never, EVER name your object reference the same as the class name. It's confusing and against most Java best practices.

[Nick Harms]

My instructions are to write a program that demonstrates the circle class by asking the user for the circles radius creating a circle object and then displaying the circles area, diameter, and circumference.

[Nick Harms]

So I could say circle shape and switch the bottom parts to shape.getcircumference for example? that's ok?

[Janeice DelVecchio]

Nick,

step by step..... what is the demo class supposed to do...... in your own words.

[Janeice DelVecchio]

Nick Harms wrote:So I could say circle shape and switch the bottom parts to shape.getcircumference for example? that's ok?

That would be preferable.

By saying

Circle.getRadius();    

it looks like getRadius is/could be a static method.

The goal should be to make code more readable and less confusing..... not just so it "just works".

[Nick Harms]

Well, the demo demonstrates the class by using its methods, It will first ask the user for their radius and then send that to the class to be used in the methods to find the information. the methods return the desired information which you call by calling the object reference and the method name, such as circle.getDiameter.

[Nick Harms]

There ya go!
I know this is probably a dumb question but i want to be sure that I dont need to change anything in the class after switching these right?

 
import java.util.Scanner;

public class CircleDemo
{
   public static void main(String[] args)
   {
      double rad = 0;
      // Create a circle object.
      Circle shape = new Circle(rad);
      
      // Create a Scanner object for keyboard input.
      Scanner keyboard = new Scanner(System.in);
      
      // Get the radius from user;
      System.out.print("Enter the radius of your circle");
      rad = keyboard.nextDouble();


      // Get data from circle and disply it
      System.out.println("The circle's area is: " + shape.getArea());
      System.out.println("The circle's diameter is: " + shape.getDiameter());
      System.out.println("The circle's circumference is: " + shape.getCircumference()); 
   }
}
   

[Janeice DelVecchio]

Nick Harms wrote: It will first ask the user for their radius and then send that to the class to be used in the methods to find the information.

Well maybe you should program it to do that....

[Nick Harms]

I thought that was what the object did? Do i simply need to move the object to after I ask them instead of before.

[Janeice DelVecchio]

Object reference names are for the reader/programmer, not the machine.

Katrina tells me frequently of someone who named their variables a, then aa, then aaa, then aaaa..... et cetera. The computer doesn't care. It will work. But how will you change/fix/debug it?

Being able to pick good reference/variable names is important.

[Janeice DelVecchio]

Nick Harms wrote:I thought that was what the object did? Do i simply need to move the object to after I ask them instead of before.

What happens if you try?

You could also do a more lazy instantiation and declare rad in the same line as setting it equal to nextDouble.

And while we're on the subject of naming things.... you might change rad to 'radius' . Letters are free and it adds to readability.

[Nick Harms]

YAY!
Thanks again, you are my hero. I knew it was something stupid!
Another AH HA! moment thanks to java ranch.

[Janeice DelVecchio]

sooo...... let's see the working product! We'll only need the demo class

[Nick Harms]

Well I know you could say double rad were it reads the input but how would you initialize it to 0 there?
Figured I might as well ask while Im here.

  
import java.util.Scanner;

public class CircleDemo
{
   public static void main(String[] args)
   {
      
      double rad = 0;
      
      // Create a Scanner object for keyboard input.
      Scanner keyboard = new Scanner(System.in);
      
      // Get the radius from user;
      System.out.print("Enter the radius of your circle");
      rad = keyboard.nextDouble();
      
      // Create a circle object.
      Circle shape = new Circle(rad);


      // Get data from circle and disply it
      System.out.println("The circle's area is: " + shape.getArea());
      System.out.println("The circle's diameter is: " + shape.getDiameter());
      System.out.println("The circle's circumference is: " + shape.getCircumference()); 
   }
}
  

[Janeice DelVecchio]

No need to initialize to zero....

  

      // Get the radius from user;
      System.out.print("Enter the radius of your circle");
      Double radius = keyboard.nextDouble();
      
      // Create a circle object.
      Circle shape = new Circle(radius);

  

This is also identical:

     System.out.print("Enter the radius of your circle");
     Circle shape = new Circle(keyboard.nextDouble());   

p.s. remember if you use 'Double' it's an object... 'double' is the primitive